According to an AMC sales catalog, the sizes for CJ-7 tires are:
P215/75R15 Goodyear Wranglers
P235/75R15 Goodyear Wrangers with white letters, both on a 15 by 7 inch rim.
The 235's are much more common and stand in at about 28.3/4 tall.
I personally run 255/70R15 and 265/70R 15 on my Jeeps for a wider tire / same heigth, without affecting the gearing.
ED